The present invention relates generally to a manually operable transmission and, more particularly, to a construction for preventing wear of the shift fork in the manipulating device for manipulating the manual transmission.
The manipulation device for a transmission to which the present invention pertains has a first fork shaft and a second fork shaft parallel to each other and carried by the case of the transmission axially movably and nonrotatably. The first fork shaft carries a plurality of shift forks axially movably and rotatably. The shift forks have engaging portions arranged in the direction perpendicular to the fork shaft. The transmission case carries also a shift and select lever shaft perpendicular to the fork shafts for axial movement and rotation. The lever shaft is held in a neutral position through a resilient member, and is provided with a retaining portion capable of selectively engaging the engaging portion of one of the shift forks. A first shift head having an engaging portion, which is in a side-by-side relation to the engaging portions of the shift forks, is fixed to the first fork shaft. The lever shaft is provided with a second retaining portion which is capable of engaging the engaging portion of the first shift head only when the first retaining portion is in engagement with the engaging portion of one of the shift forks on the first fork shaft. At the same time, a single shift fork is fixed to the second fork shaft. Also, a second shift head having an engaging portion in a side-by-side relation to the engaging portion is fixed to the second fork shaft. The first retaining portion of the lever shaft is selectively engageable with the engaging portion of the shift head. With this arrangement, a shift fork axially movably and rotatably mounted on the first fork shaft functions as a means for preventing the rotation of the fork shaft through engagement with the sleeve of the clutch mechanism of the transmission. This arrangement, therefore, is much more reasonable as compared with the conventional arrangement in which a shift fork as a separate means is splined to the fork shaft to prevent the rotation of the shift fork. Namely, in the known arrangement in which the shift fork is splined to the fork shaft to prevent the rotation of the shift fork, there is a problem in terms of precision of machining. More specifically, there is a tendency that a play is formed in the fitting portions and friction in the fitting portion tends to grow, resulting in a deteriorated feeling in shifting manipulation, as well as high cost of production. This problem, however, can effectively be eliminated in the transmission manipulation device to which the invention pertains since rotation of the shift fork is prevented by arranging such that the shift fork is rotatably fitted to the fork shaft and is caused to engage with the sleeve of the clutch mechanism. It will be seen that this arrangement to which the invention pertains is quite reasonable in this regard. This arrangement, however, suffers from the following disadvantages. Assuming here that the shift and select lever shaft is manipulated for selection and shifting against the resilient force of the resilient member for biasing the lever shaft to the neutral position, the resilient member naturally develops a repulsive force. If this repulsive force is borne by the shift fork on the first fork shaft as in the case of the conventional arrangement, the repulsive force tends to rotate the shift fork on the first fork shaft to bring the shift fork into close contact with the sleeve of the clutch mechanism. In consequence, an abnormal wear is caused in the circumferential region of the shift fork contacting the sleeve as the sleeve rotates.